Now action speed of electric circuits is approaching that of optical transmission circuits. However a principle barrier to increase action speed of the electric circuits is higher than that to increase action speed of optical transmission circuits operational speed. This is because time constant due to static electric capacity associated with electric circuits increases by the high speed action. Therefore, research and development is actively conducted on fusion of electric circuit and optical circuit to partly compensate a high speed action of electric circuit with an optical transmission path.
Specifically, VCSEL (Vertical Cavity Surface Emitting Laser) is installed in an electric circuit substrate and light signal emitted there is injected into an optical fiber and optical waveguide to propagate, and the light signal is received with installed PD (Photodiode) to transmit. Studied is a method for embedding an optical fiber and an optical waveguide into an electric circuit substrate itself, and a method employing an optical fiber and an optical waveguide as substitute for an existing electric cord between plurality of electric circuit substrates. And, for example, an organic waveguide sheet (a polyamide waveguide sheet is a typical waveguide sheet) and an optical fiber sheet are proposed.
VCSEL is a surface emitting laser and the laser emits in a vertical direction with respect to the installed electric circuit substrate. When the electric circuit substrate is installed in a vertical direction, the laser emits in a parallel direction with respect to the electric circuit substrate. Such laser installation killing advantages of high-density multiple installation of VCSEL is not generally utilized.
Further, since the optical waveguide and the optical fiber which are embedded in the electric circuit substrate waveguide in parallel with the electric circuit substrate, 90 degree change of an optical waveguide direction is required to combine the laser emit from VCSEL with these optical waveguide and optical fiber.
With regard to such a method for changing 90 degree direction of optical waveguide, studied are a method comprising steps of grinding end surfaces of optical fiber and waveguide at 45 degree and forming mirror by subjecting metal vapor deposition to change 90 degree, and a method of changing with a mirror having 45 degree angle.
Further, it is different from necessity of 90 degree direction change of optical waveguide in application region, but for example with FTTH in which optical fibers are wired in users' houses, it is necessary to secure a space for gently bending optical fibers in room corners and hole portions through which the optical fibers pass from outside to inside the house general fibers can not be bent in less than several cms due to problems of mechanical characteristic and optical characteristic, thereby ended up spoiling interior arrangement and landscape. Correspondingly, optical fibers capable of being bent mechanically and optically even at the minimum bend radius of 15 mm have been developed recently.
Further, as an application of converting optical waveguide direction with ultraminiatur, a method of reducing the specified portion of the optical fiber into extremely minute diameter and bending it is proposed and commercialized. In this method in which the reduced portion of the optical fiber diameter is about several μm to 10 μm, even if this fine optical fiber is bent at a radius of 1 mm, a bend distortion due to the bend becomes not more than 1%, thereby the optical fiber can be sufficiently mechanically bent. Further although it is not a configuration where light is confined with fiber of this fine portion alone, a relation between light and environment (air) is referred to a relation between core and clad in combination of this fine optical fiber and its exterior environment, i.e. air. And it functions as a waveguide equivalently having ultra high equivalent refractive index difference of several tens % and even with a minute bend radius it can be bent without light loss.    Patent Reference 1: U.S. Patent publication No. 2203/0165291A1    Patent Reference 2: U.S. Pat. No. 5,138,676    Patent Reference 3: Japan Laid-open Unexamined Patent Publication 2000-329950    Non Patent Reference 1: Ohki et al. “Development of 60 bps Parallel Optical Interconnect Module (ParaBIT-IF)” IEICE 2000 Technical Report EMD2000-7)    Non Patent Reference 2: Shimizu et al. “Optical I/O Built-in System LSI module (3) Design of Optical Coupling System” IEICE 2003 Electronics Society Convention C-3-125    Non Patent Reference 3: Sasaki et al. “Optical I/O Built-in System LSI module (5) Development of Substrate implementation Connector Optical coupling System Design” IEICE 2003 Electronics Society Convention C-3-127